CJC_H1_CHEM_P2 Prelim

8872/02/CJC Prelim 09 1 Name Class: 2T CATHOLIC JUNIOR COLLEGE CHEMISTRY 8872/02 Higher 1 Paper 2 Preliminary Examination 2009 2 hours Candidates answer Section A on the Question Paper and Section B on separate paper. Additional Materials: Paper Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and class on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagrams, graphs or rough working. Do not use paper clips, highlighters, glue or correction fluid. Section A Answer all questions. Section B Answer any two questions on separate answer paper. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Section A B5 B6 B7 Total There are a total of 10 printed pages including this cover page.

8872/02/CJC Prelim 09 2 Section A Answer all the questions in this section in the spaces provided. 1 (a) The decomposition of hydrogen peroxide is a first order reaction. H 2O2 H 2O + ½O 2 The activation energy of the forward reaction is 1 80 kJ mol -1 and that for the reverse reaction is 282 kJ mol -1. The rate of the reaction can be increased by the addition of platinum catalyst. (i) Use the data provided to construct a reaction p athway diagram for the uncatalysed reaction, indicating the activation energy of the forward reaction. (ii) Calculate the enthalpy change for the decompos ition of hydrogen peroxide. ΔH = __________________ (iii) State how the reaction pathway diagram will c hange with the addition of platinum catalyst. (iv) Use the bond energies given in the Data Booklet to calculate another value for the enthalpy change for the decomposition of hydrogen peroxide. (The structure of H 2O2 can be taken as: H-O-O-H) (v) Suggest a reason for the discrepancy between th e values in (a) (ii) and that in (a)(iv). [7]

8872/02/CJC Prelim 09 3 (b) Wine contains a small amount of sulfur dioxide that is added as a preservative. The sulfur dioxide content of the wine can be determined by the following method. A 50 cm 3 sample of wine is reacted with 40 cm 3 of 0.01 mol dm -3 of aqueous iodine which is present in excess. The unreacted iodine requires 23.60 cm 3 of 0.02 mol dm -